Synopsis: There is no substitute for pure electric range.
The greater the battery capacity:
- The greater the distance that can be driven before the battery would require replacing.
- The less time to add charge to drive a given distance.
- The better the potential vehicle performance.
Here is the slightly overview explanation, together with the implications for hybrid vehicles, with the sections below giving more details.
Firstly, the total distance a battery can power a vehicle can be calculated by:
- charge cycles x range.
This means for any given battery technology, an EV with half the battery size would logically only be able to travel half the total distance during the life of the battery, but halving the efficiency will also result in the same loss of total distance a vehicle can travel in the life of the battery. Overall, the range of a vehicle together with battery chemistry and measures to maximize battery life determine more than just range alone.
The second side effect of battery size is charging speed.
Any increase in battery size will yield as similar increase in potential charging speed. With the same battery technology, as battery size increases, the time required to add a given amount of charge decreases. While the time to fully charge the battery is the same, half charging a double sized battery will give the same range as fully charging a battery of the original size.
Third, and often overlooked is that batteries are not only limited in their charging speed, but also their discharging speed, which dictates the performance potential under electric power. The discharging speed determines the maximum power available to power electric motor(s) of an EV. A smaller battery dictates a less powerful electrical powertrain.
The implications for hybrids and plug in hybrids, are that kilometres travelled per amount of battery are actually going to be no better than with full EVs, and the argument that for example “hybrids could enable building 5x the number of vehicles for a given battery production capability”, is really only valid if those vehicles will be powered by fossil fuels 80% of the time, or will have their batteries replaced during their lifetime.
Increasing battery size will at least give a similar increase in charging speed.
A battery is made from a number of cells, and each cell can be charged at a given rate.
Imagine a battery with 50 cells, where each cell has a capacity of 1kWh and be charged at a rate of 1kW, which means each cell takes 1 hour to charge. A 50kW charger would be needed to be able to charge every cell simultaneously, so with a 50kW capable charger, 50 cells of the battery can be charged in 1 hour.
Now consider a 100-kWh battery that is made from the same type of cells, which would require 100 cells. Now a 100-kW charger would be required to supply sufficient power to charger all cells simultaneously. Even with the 100-kW charger, it will still take 1hr to fully charge the battery even though it is being charged at twice the speed. But now a full charge of the battery can provide double the range, and only a half charge is required to hold 50 kWh. Since to gain 50kWh of charge and then be able and travel the distance, the EV can travel with 50kW, the larger battery would only need 1/2 hr of charge!
Reality is a little more complex, with both bad news and good news.
The bad news is that unless new technology enables making the cells lighter in weight, the extra weight from the larger battery will make the EV a less efficient, so a little more than 1/2 the charge of the larger battery will be needed for the same range unless the larger battery can use some new technology.
The good news is that in practice, batteries cannot be charged at the same speed all the way from empty to full, with low charge speeds at near empty, and typically particularly slow charge speeds from around 85% until fully charged. This is good news when half-charging a battery, since it must avoid at least one of the slower charging points, so in reality, a battery can be more than 50% charged in 50% of the time it takes for a full charge.
In practice, a double size battery can be charged for the same range in less than half the time, and any increase in battery size will translate to at least a similar decrease in the time required to gain the same amount of charge as the original sized battery.
Note this is potential charging speed at high-speed fast chargers. ‘Slow charging’ in the background, such as while parked at home, is normally by the power available, and not by the ability of the battery to accept charge.
The Hybrid and Plugin Hybrid Limitation.
(Note, the plan is to add links to claims by manufacturers)
Hybrids or “self-charging hybrids”, mostly only make use of the battery when accelerating or decelerating, and with a battery usually typically around 5% of the size of a full EV, if the hybrid obtains more than 5% of its power from the battery, then that battery will have a shorter life than the battery of the full EV.
This can be an even more significant limitation with PHEVs, which do have larger batteries, but in theory offer the promise of only needing ICE power when on longer road trips, when the EV power only range is insufficient. However, with a battery of anywhere between 20% and 50% of than range of a typical full EV, a very short battery life could result if the owner actually succeeds in doing the bulk of their driving on battery power alone.
Updates.
More details and explanations to be added.
- 2023 April 13 th: preliminary version.